Semiconductor devices are extremely important products used in diverse products ranging from industrial use to home use. A semiconductor chip which constitutes the semiconductor device is manufactured by, for example, forming various circuits on a silicon wafer and cutting the wafer into the chips of predetermined size.
In a semiconductor manufacturing process where various circuits are formed on a silicon wafer, a wafer heating apparatus is used to heat the semiconductor wafer such as silicon wafer (hereinafter referred to simply as wafer) when forming a thin film of semiconductor, etching the film and baking the resist film.
Conventional semiconductor manufacturing apparatuses can be divided into batch operation type which heats a plurality of wafers simultaneously and sequential operation type which heats the wafers one by one. The sequential operation type has an advantage that the temperature can be controlled more accurately, although it can process less wafers at a time. While the use of semiconductor heating apparatuses of the batch operation type has been predominant in the past, use of semiconductor heating apparatuses of the sequential operation type where the wafers are processed one by one has been increasing as the wafer size increases from 8 inches to 12 inches while wiring of the semiconductor devices becomes finer and higher accuracy is required in controlling the wafer processing temperature.
When the sequential operation type is employed, however, it is required to reduce the time taken to process each wafer since the number of wafers processed at a time decreases. Therefore, there is a strong demand for the wafer heating apparatus to reduce the time required in cooling down as well as in heating. Accordingly in the wafer heating apparatus, it is a common practice to place a heater section, comprising a plate-shaped member which has a resistive heating member, in a casing and provide a cooling nozzle in the casing so as to forcibly cool the heater section by supplying a cooling medium from the nozzle (Japanese Unexamined Patent Publication (Kokai) No. 2003-100818 and Japanese Unexamined Patent Publication (Kokai) No. 2004-063813).
Recently wafer heating apparatuses made of ceramics are widely used as the wiring of the semiconductor devices becomes finer and higher accuracy is required in controlling the wafer processing temperature.
The wafer heating apparatuses made of ceramics are disclosed in, for example, Japanese Unexamined Patent Publication (Kokai) No. 2001-135684, Japanese Unexamined Patent Publication (Kokai) No. 2001-203156, Japanese Unexamined Patent Publication (Kokai) No. 2001-313249 and Japanese Unexamined Patent Publication (Kokai) No. 2002-76102. FIG. 19 shows a wafer heating apparatus 171 made of ceramics disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2001-203156.
The wafer heating apparatus 171 made of ceramics comprises a plate-shaped ceramic member 172 and a casing 179 as the major components, wherein the plate-shaped ceramic member 172 made of nitride ceramics or carbide ceramics is secured to the opening of the bottomed casing 179 made of a metal such as aluminum, by means of bolt 180 via an insulating connecting member 174 made of a resin, of which top surface is used as a mounting surface 173 to mount the wafer W thereon, and a resistive heating member 175 having concentric configuration as shown in FIG. 20 is provided on the bottom surface of the plate-shaped ceramic member 172 thereby forming a heater section.
With this configuration, a cooling medium is injected from a nozzle 182 into a space delimited by the plate-shaped ceramic member 172 and the casing so as to circulate and is discharged through a discharge port 183, thereby cooling the heater section.
In order to form a uniform film over the entire surface of the wafer W or provide uniform heat-reaction condition of the resist film by using the wafer heating apparatus 171 made of ceramics of such a constitution, it is important to make the temperature distribution uniform by minimizing the temperature difference across the surface of wafer, and it is necessary to heat and cool down the wafer in a short period of time. In addition, it is necessary to change the temperature setting of the wafer heating apparatus 171 in order to vary the wafer temperature, and it is required to heat the wafer heating apparatus 171 made of ceramics in a short period of time and cool it down in a short period of time.
Japanese Unexamined Patent Publication (Kokai) No. 2002-83848 discloses that disturbance of the flow of the cooling medium can be mitigated by keeping the surface roughness of the bottom surface of the casing within a predetermined value, and that it is made possible to improve the efficiency of heating and cooling.
Japanese Unexamined Patent Publication (Kokai) No. 2002-100462 discloses that heating rate and cooling rate of the wafer can be increased by controlling the heat capacity of the wafer heating apparatus 171 made of ceramic to 5000 J/K or less. However, the casing 179 has a heat capacity 3.3 times that of plate-shaped ceramic member 173 or more, and the ratio S/V of the surface area S of the casing 179 to the volume V of the casing 179 is less than 5 (1/cm), and therefore the cooling time cannot be sufficiently reduced.
Thus it has been taking relatively long time to change the set temperature of heating the wafer with any of the prior art technologies, and there has been a demand for a wafer heating apparatus capable of changing the temperature in a shorter period of time.
In the meantime, it has been in practice to decrease the temperature difference across the surface of wafer by controlling the distribution of resistance of the resistive heating member 175 having band shape or controlling the temperature of the resistive heating member 175 having band shape separately, and it has been proposed to increase the amount of heat generated from the surrounding area in the case of a structure susceptible to heat sink.
But any of the proposals have problems that a very complicated structure and complex control are required, and there is a demand for a wafer heating apparatus capable of heating with uniform temperature distribution with a simple structure.
Moreover, since the wafer heating apparatus 171 is vulnerable to the light, heat, processing gas and other influences when used in a semiconductor manufacturing apparatus, the resistive heating member 175 is required to have durability against oxidization and other attack on the surface. For this reason, it has been proposed to coat the resistive heating member 175 with an insulation layer on a part or whole of the surface thereof, so as to improve the durability of the resistive heating member 175 (refer to Japanese Unexamined Patent Publication (Kokai) No. 2001-297857).
Since the insulation layer can also serve as a heat insulator for the resistive heating member 175, it may make an obstacle in quickly cooling down the wafer heating apparatus 171 which has been heated. Therefore, there has been a wafer heating apparatus where surface roughness Ra of the insulation layer is controlled in a range from 0.01 to 10 μm in an attempt to improve the cooling effect (refer to Japanese Unexamined Patent Publication (Kokai) No. 2001-297858).